Some filtration operations are carried out with filters, particularly filters made of a granular filtering material, the structure of which is generally reinforced concrete and includes, primarily, a bed plate which bears on shells or walls about the periphery and a perforated floor supporting the filtering material.
This bed plate is perforated for allowing the passage and flow of the liquid, particularly water, which is filtered by the material, as well as the passage and distribution of the washing fluids. For so doing, it includes a sufficiently high number of openings provided with recovery members for the filtered liquid and for the distribution of the washing fluids. Moreover, this floor has to be designed and made in such manner as to support large vertical forces which alternately descend and ascend. Therefore, the floor structure has to include sufficient anchoring elements for accommodating these alternating forces.
The present invention relates to a method for making the floor of these filters.
The known techniques consist in the assembly of small dimensional prefabricated slabs. These slabs which are prefabricated in the workshop or at the site are put in position and connected to the support elements and are connected to each other by a system of plates and bolts used for anchoring purposes. A seal is then made between each of the slabs and the periphery of the filter in order to ensure tightness.
This system of plates, sealing stems and bolts involves a costly connection process, which is not satisfactory from the mechanical point of view and is difficult to practice. Moreover, the seal which is delicate and difficult to make necessitates skilled labor.
Another technique consists in making some floors by casting a reinforced concrete slab on a bottom layer such as a plastic shuttering, called a permanent shuttering, which is previously put in position on the filter supports.
Due to the forces to which it is subjected, this floor has to be either of a large thickness, in which is necessary to reinforce the shuttering which has a very reduced mechanical strength with a complex reinforcing system, which is costly, or it requires a system including very close supports, with very short spans between the supports and is therefore also very costly.